Motivating fluid vacuum pump

ABSTRACT

The invention relates to a driving agent vacuum pump used in microsystems technology, comprising an evaporator chamber and a pump chamber that are separated by a jet arrangement. The design of the driving agent vacuum pump is improved by: a planar arrangement of at least one jet, which extends vertically in depth and which is situated between two, in particular, parallel plates, these plates closing the evaporator chamber and the pump chamber; an opening in the pump chamber, preferably above the jet arrangement, for drawing in a medium to be pumped, and; an opening for expelling a preferably compressed gas underneath the jet arrangement.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of and claims priority toInternational Patent Application No. PCT/EP2005/011660 filed on Oct. 31,2005, which claims priority to German Patent Application No. 10 2004 053006.8 filed on Oct. 29, 2004, subject matter of these patent documentsis incorporated by reference herein in its entirety.

FIELD OF THE INVENTION

The invention concerns a miniaturized driving agent vacuum pump whichuses preferably planar jet and pump wall geometries structured inkeeping with microsystem technology and a suitable driving agent forvacuum creation. It is distinguished by simple manufacturability, smallsize and thereby good integration capability, for example into mobilesystems, operation in a pressure region extending from about oneatmosphere to several Pascal, higher suction efficiency and positionindependent functionality.

BACKGROUND OF THE INVENTION

Pumps for the transport of gases or for the creation of a vacuum existin macroscopic scale in a number of type variations: displacement pumps,molecular pumps, sorption pumps, condensors, kyro pumps and drivingagent pumps. Each of these varieties is suited for application within aspecific pressure region; to create a pregiven pressure it can benecessary to operate a number of these pumps in series. The sizes ofthese customary vacuum pumps even in their smallest construction formslie in the area of several tens of cubic centimeters. Therefore thesepumps cannot be sensibly integrated into systems with microcomponents(for example, sensors). The application of, for example, miniaturizedanalysis devices, which for their function require a vacuum pressure ora constant gas flow is therefore closely coupled to the development ofsuitable micro gas pumps.

Micropumps use different physical or chemical principles to create apumping effect (see: Nam-Trung Nguyen, Xiaoyang Huang, Toh Kok Chuan,MEMS-Micropumps: A Review, Transactions of the ASME, Vol. 124 (June2002), 384-392; P. Woias, Micropumps—summarizing the first two decades,Proc. SPIE, Vol. 4560 (2001), 39-52). Many of the systems are limited intheir application to liquid medium; only a few suit themselves to thepumping of gases or to the creation of a vacuum.

A scaling of the customary pump principles with rotating parts for thedisplacement of gases is, because of the very small measures and therequired rotational speeds for the creation of the displacement, nearlyimpossible. Most of the realized microvacuum pumps are based however onmechanically movable parts which considerably influence the long timestability of such systems, such as membranes, which through theirmovement create by way of different actuators the evoked pumping effector in part require active or passive valves (see: R. Rapp, W. K.Schomburg, D. Mass, J. Schulz, W. Stark, LIGA micropump for gases andliquids, Sens. Act. A. Vol. 40 (January 1994), 57-61; R. Linnemann, P.Wias-P, C. D. Senfft, J. A. Ditte rich, A self-priming andbubble-tolerant piezoelectric silicon micropump for liquids and gases,Proc. MEMS 1998 Heidelberg, 532-537; C. G. J. Schabmueller, M. Koch, A.G. R. Evans, A. Brunnschweiler, M. Kraft, Design and fabrication of aself-aligning gas/liquid micropump, Proc. SPIE-Int. Soc. Opt. Eng.(USA), Vol. 4177 (2000), 282-90).

Also capable of finding application are alternative pumps withoutmechanical parts and which are based on the principle of Knudsencompressors (thermal transpiration, thermal molecular pressure): betweenthe two volumes at different temperatures which are connected to oneanother by way of a channel with a small cross sectional area, thereexists a pressure difference which can be used for the creation of apumping effect. Disadvantageous of this however is the relativelycomplicated construction and the high surface area requirement of suchsystems, indeed because of the low achievable compression ratio, manysuch pumps need to be driven in a series in order to create the desiredsuction performance and pressure difference (see: R. M. Young, Analysisof a micromachine based vacuum pump on a chip actuated by thermaltranspiration effect, J. Vac. Sci. Technol B17(2), March/April 1999; J.P. Hobson, D. B. Salzman, Review of pumping by thermal molecularpressure, J. Vac. Sci. Technol. A 18(4), July/August 2000, S. E. Vargo,E. P. Muntz, Initial Results from the first MEMS fabricated thermaltranspiration-driven vacuum pump, Rerefied Gas Dynamics: 22. Int.Symposium, 2001).

The use of the pumping principle forming the basis of the invention isnot known in micropumps.

SUMMARY OF THE INVENTION

The micropump of the invention uses the functional principle of drivingagent pumps described in DIN 28 400, part 2, which principle is based ona rapidly flowing vapor phase or liquid driving agent expanded by movingthrough a jet. The gas particles in the container to be evacuated moveinto this driving agent stream and while in that stream receive impactswith the driving agent molecules giving them impulses in the pumpingdirection.

A special standing among driving medium pumps is taken by diffusionpumps, in the case of which, in contrast to other stream pumps, themixing process of the driving agent with the gas to be evacuated doesnot occur in a turbulent boundary layer, but takes place by diffusion ofthe gas into the driving stream.

In FIG. 1, by way of example the pumping principle for all driving agentpumps is illustrated by the aid of the construction of a diffusion pump:in a boiling space 12, by way of a heater 11, a suitable driving agent(for example silicon oil) is heated; the resulting driving agent vapor14, escapes at supersonic speed from the jets 15, and transmitsdownwardly directed impulses onto the molecules of the gas 18 to beevacuated. The driving agent vapor stream 17 condenses on the cooledwalls of the pump body 16 and is returned again to the supply container12.

The gas molecules retain their impulses and moving with the vapor streamreach the next lower jet stage. Below these last jets the gas is takenaway through the fore vacuum pipe 13, by means of a fore pump. Thepumped away gas is further compressed from stage to stage, so that inthe case of a constant mass flow its volume flow is correspondinglyreduced; the pump area between the jets and the wall likewise diminishesaccordingly from top to bottom, and the highest permissible pressure atthe fore vacuum side is hereby increased (see: Wutz, Adam, Walcher,Theorie und Praxis der Vakuumtechnik, Vieweg Verlag Braunschweig, 5.Edition (1992)).

The novelty of the invention lies in the conversion of this principleinto a miniaturized form, preferably into a planar form adequate formicrosystem techniques. Resulting from this utilization ofminiaturization are further advantages. Here, in the case of the drivingagent vacuum pump, consisting of an evaporating chamber at high pressureand a pump chamber at low pressure, separated by a jet arrangement, itis provided that the pumping effect is achieved by a flow at high speedthrough a preferably planar arrangement of jets vertical in depth andlocated between two parallel plates which close the chambers in the jetregion. Further an opening is provided in the pump chamber above the jetarrangement to draw in the medium to be pumped and an opening for thedischarge of the compressed gas is provided below the jet arrangement. Aplanar jet arrangement made of, for example, one or two Laval jets isused, for a purpose of expanding and accelerating selectively up tosupersonic speed a liquid, gas or vapor phase driving agent underpressure. With this the jet stream can achieve supersonic speed.

Because of its small dimensions the driving agent vacuum pump is usableat high pressures from about one atmosphere. By choice of the number ofjets arranged below one another and therewith a number of pressuresteps, high compression ratios are achievable. Furthermore by the choiceof suitable dimensions for the pump, of the driving agent and of theevaporating temperature, the working pressure range can be variedwidely.

A condensable medium or a gaseous medium is used as the driving agent.Further, as the driving agent a liquid is used with in oneimplementation the liquid driving agent being evaporated by a heater inthe form of an electrically heated coil arranged in the evaporatingchamber. Alternatively the driving agent is already delivered to theevaporating chamber in gaseous form.

The increased pressure of the driving agent inside of the jetarrangement can be achieved either by suitable measures outside of themicropump or in the case of a vapor phase driving means by way of aheater and evaporator integrated in the pump so that a liquid can beachieved. The scaling of the measurements of the pump into the region ofthe free path of the gas molecules in the pressure region makes possiblean operation in a pressure region of about one atmosphere down toseveral Pascal.

To achieve a high as possible pressure difference with only onemicrodriving agent pump several jet stages can be operated behind oneanother so that the evacuated gas in each stage is further compressed. Avariation of the used driving agent and of the used evaporationtemperature likewise makes possible an operation in different pressureregions.

To avoid a contamination of the jets or of the jet delivery channels bysmall particles, a particle filter can, for example, be integrated inthe evaporation chamber. A similar filter can also be integrated intothe delivery and discharge channels at the input and output of theevaporating chamber.

The driving agent ejected from the jets, which produces the actualpumping effect, in the case of the use of gases or liquids can betransported in a suitable way from the pump, and in the case of the useof a vapor phase driving agent it can be condensed on the pump wallsand, as the case may or may not be, can then be returned to the heaterintegrated in the pump. There it is again vaporized and it transitionsinto a driving agent circuit to make possible a closed system suppliedoutwardly with only energy for the heater.

To condense a gaseous driving medium the vacuum pump is provided withcooling of the outer wall of the pump chamber. The condensation of thevapor phase driving agent can for example be accomplished by way ofchannels in the walls or by cooling ribs, which are filled with a liquidor a gas which removes heat from the sidewalls used for thecondensation; alternatively for this also Peltier elements can be used.

Moreover, in a further development a connection is provided between theevaporating chamber and a pump chamber through which a condensed drivingagent is returned and which connection at the same time serves as apressure stage. A return of the condensed driving agent from the pumpchamber to the evaporating chamber can, for example, be carried out byone or more capillary shaped channels which is or are covered by a layerhaving an outer surface energy higher than that of the pump chamber.These measures make it possible to operate the micropump independentlyof its position.

For monitoring the pumping function in the pump chamber at its input oroutput, or in the evaporating chamber or in several or all positions apressure measurement is integrated with the pump. To monitor theoperation of the micro driving agent pump and, as the case may be, tocontrol or regulate it, several pressure sensors can be integrated intothe pump. These pressure sensors can be applied to the pumping chamberat the high vacuum side and the fore vacuum side, as well as to theevaporating chamber and by means of suitable switching technologymeasures can detect the pressure difference between the mentionedmeasuring points.

Because of their good reliability and applicability to differentpressure regions, as pressure sensors are offered, for example, a systembased the Pirani principle which measures the pressure dependent heatconductibility of the surrounding medium (see: Wutz, Adam, Walcher,Theorie und Praxis der Vakuumtechnik, Vieweg Verlag Braunschweig, 5.Edition (1992); Mastrangelo, Muller, Microfabricated ThermalAbsolute-Pressure Sensor with on-Chip Digital Front-End Processor, IEEEJ. Solid State Circuits, Vol. 65 No. 2 (1994), 492-499, Puers,Reyntjens, Bruyker, The NanoPirani—an extremely miniaturized pressuresensor fabricated by focused ion beam rapid prototyping, Sens. & Act. A.Vol. 97-98 (2002), 208-214). With this, there results a pressuremeasurement by way of a Pirani arrangement integrated into a microsystemtechnique.

Likewise for monitoring the pump and for determining the suctionperformance a flow measurement based for example on a microsystemtechnique realized heating wire principle can be made at the suctionintake pipe (suction intake region) and/or possibly at the outlet.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectioned schematic illustration of a diffusion pump.

FIG. 2 is a schematic perspective view of a micro agent driving pump.

DETAILED DESCRIPTION

The construction of the invention consists, for example, of threesubstrates of which the middle substrate contains the jet structures andit is distinguished by a high heat conductibility in order to facilitatethe evaporation and condensation of a liquid driving agent.

In one implementation the system or the driving agent vacuum pump ismade of three substrates, the middle substrate of which because of itsgood heat conductibility, mechanical and chemical stability as well asits structurabilty is preferably structured by way of anisotropicetching methods, is silicon and the substrates which close its two sidesare preferably because of its low thermal conductivity made ofanodically bonded glass.

Moreover, in this further implementation it is advantageous if themiddle substrate because of its good heat conduction is made of agalvanic metal structure, for example one made by UV-Liga technique,preferably galvanically washed on to a lower glass substrate and anupper glass substrate as a seal.

The two outer substrates can contain needed connection channels and, asthe case may be, can serve as carriers for the integrated pressure orflow sensors and to close the evaporating chamber and the pumping space.To serve as substrates silicon, preferably anisotropically structuredboron silicate glass, can be used because of its good chemical andmechanical stability, and even galvanically finished metal structuresand glass substrates or structures made by injection molding processesand polymer substrates can be used.

The driving agent vacuum pump according to the invention is preferablyclosed by polymer substrates and also the jet arrangement is created by,for example, an injection molded structure.

Because of its small size the microdriving agent pump has the followingadvantages: the pump can be used for existing or in the future developedminiaturized systems, without necessarily increasing their constructionshape.

Further, the micro driving agent pump because of its small internalmeasurements can be used below a pressure of about one atmosphere and,according to its implementation with several jet stages and a suitabledriving agent, a pressure of down to several Pascal can be reached.

The system distinguishes itself by a simple way of being manufactured:in the first case the micro driving agent pump consists of a siliconsubstrate structured by plasma etching methods and two anodically bondedboron silicate glass substrates as covers above and below the siliconsubstrate, one of which boron silicate glass substrates provides anaccess from the outside into the evaporating chamber for the externalsupply of a driving agent.

One such system is shown in FIG. 2 by way of example: through theopening 3, a vapor phase driving agent is delivered, which is expandedthrough the jets 5, and provides impulses onto the gas moleculesdelivered to the high vacuum side 6, through channel 7, connected to avolume. The driving agent condenses on the water cooled side walls ofthe pump 3, and the evacuated gas molecules move out of the micropumpthrough the vacuum fore side 2, and the outlet 1.

Typically the side length of the system has a value of about 15 mm.

1. A driving agent vacuum pump, especially of microsystem technique, comprising; an evaporation chamber and a pumping chamber, which are separated by a jet arrangement; a planar arrangement of at least one jet running obliquely, preferably vertically, in depth between two, especially parallel, plates, with the plates covering the evaporation chamber and the pumping chamber, and by an opening in the pumping chamber preferably above the jet arrangement, for taking in an agent to be pumped and by an opening for driving out a, preferably compressed, gas below the jet arrangement, said driving agent vacuum pump further including a heater, preferably in the form of an electrically heated coil arranged in the evaporation chamber.
 2. A driving agent vacuum pump according to claim 1, wherein at least one jet is formed as a Laval jet.
 3. A driving agent vacuum pump according to claim 1, wherein the jet arrangement has several jets.
 4. A driving agent vacuum pump according to claim 1, wherein the driving agent is at least one of a condensable medium, a gaseous medium and a liquid.
 5. A driving agent vacuum pump according to claim 1, wherein the driving agent is delivered into the evaporation chamber as a gas.
 6. A driving agent vacuum pump according to claim 1, wherein the pumping chamber is provided with cooling.
 7. A driving agent vacuum pump according to claim 6, wherein the cooling includes channels or cooling ribs.
 8. A driving agent vacuum pump according to claim 6, wherein the cooling is formed by at least one Peltier element.
 9. A driving agent vacuum pump according to claim 1, wherein between the evaporation chamber and the pumping chamber is a connection through which a condensed driving agent is returned.
 10. A driving agent vacuum pump according to claim 9, wherein the connection is formed capillarily.
 11. A driving agent vacuum pump according to claim 9, wherein the capillaries are covered by a layer having a higher outer surface energy than the pumping chamber to control the return flow of the driving agent.
 12. A driving agent vacuum pump according to claim 1, wherein a pressure sensor for monitoring the pumping function in the pumping chamber, said pressure sensor being integrated into the pump and located in at least one of the pump input, the pump output and in the evaporating chamber.
 13. A driving agent vacuum pump according to claim 12, wherein the pressure sensor measures pressure using a Pirani arrangement preferably integrated into the microsystem.
 14. A driving agent vacuum pump according to claim 1, further including a flow measurement for determining the vacuum performance, the flow measurement being provided, in at least one of the vacuum intake region and the output region.
 15. A driving agent vacuum pump according to claim 14, wherein the flow measurement is made using a heated wire principle, preferably integrated into the microsystem.
 16. A driving agent vacuum pump according to claim 1, further including at least one particle filter for reducing contamination, the particle filter being located in at least one of the jet supply channels, the evaporation chamber and the delivery and exhaust channels at the input and output.
 17. A driving agent vacuum pump according to claim 1, wherein the pump is made of three substrates.
 18. A driving agent vacuum pump according to claim 17, wherein a middle substrate consists of a silicon substrate, preferably structured according to an anisotropic plasma etching method, and in that two side substrates are made of glass, preferably anodically bonded.
 19. A driving agent vacuum pump according to claim 18, wherein the middle substrate is made of a metal structure, preferably galvanically finished.
 20. A driving agent vacuum pump according to claim 19, wherein the middle substrate is galvanically washed onto a lower glass substrate and has an upper glass substrate as a closure. 